As a steering support structure of an automobile, an instrument panel reinforcement pipe (herein after also referred to as “instrument panel R/F pipe”), a floor brace, and a cowl-to brace are used. These members are also collectively referred to as an “instrument panel R/F structure,” and form a part of a skeleton structure of the automobile.
The instrument panel R/F pipe is a circular tubular pipe member, extends along a width direction of a vehicle, and respective ends thereof are fixed on front pillars. The floor brace is a support member which primarily supports the instrument panel R/F pipe in an up-and-down direction of the vehicle, and has a lower end fixed on a floor tunnel, and an upper part connected to the instrument panel R/F pipe. The cowl-to brace is a support member which primarily supports the instrument panel R/F pipe in a front-and-rear direction of the vehicle, and has a front end fixed on a cowl panel placed at a farther front side of the vehicle than the instrument panel R/F pipe, and a rear part connected to the instrument panel R/F pipe.
For example, as exemplified in FIG. 10, in JP 2016-120866 A, attachment positions of a floor brace 100 and a cowl-to brace 102 onto the instrument panel R/F pipe 104 are coincident in the width direction of the vehicle (RW direction in FIG. 10). In FIG. 10, an example vehicle is shown in which the steering wheel is on the left side. More specifically, as exemplified in FIG. 10, a bracket 105 is joined by welding or the like to a part of the instrument panel R/F pipe 104 at its circumference. In addition, a rear end of the cowl-to brace 102 is fixed to the front end of the bracket 105. Further, an upper end of the floor brace 100 is fixed to a rear end of the bracket 105.
Moreover, a steering column 106 is placed to incline from an upper side toward a lower side of the vehicle in a side view from the rear of the vehicle toward the front of the vehicle. In this state, the steering column 106 is supported by the instrument panel R/F pipe 104 via a support member such as a steering support 108.
By attaching the floor brace 100 and the cowl-to brace 102 onto the same location on the instrument panel R/F pipe 104, it becomes possible to suppress up-and-down wobbles (staggering) of the steering wheel 110 with superior balance.
For example, when a vehicle body falls into a large hole on a road surface or moves out of such a large hole, or when the vehicle rapidly passes a projected step, an up-and-down load is applied on the steering wheel 110, which is a heavy-weight object.
In this case, as shown in FIG. 11, when a downward load F1 is applied to the steering wheel 110, for example, a torsion moment Tq1 (torque) is applied to the instrument panel R/F pipe 104 in a clockwise direction from its center axis. The torsion moment Tq1 acts to compress the floor brace 100 toward a lower side of the vehicle. With this process, a stress in the opposite direction is caused at the floor brace 100, and, as a result, a torsion stress Tq1a in an opposite direction from the torsion moment Tq1 is generated in the instrument panel R/F pipe 104.
As shown by a broken line, when an upward load F2 is applied to the steering wheel 110, a torsion moment Tq2 (torque) is applied to the instrument panel R/F pipe 104 in a counterclockwise direction from its center axis. The torsion moment Tq2 acts to compress the cowl-to brace 102 toward a front direction of the vehicle. With this process, a stress in an opposite direction is generated in the cowl-to brace 102, and, as a result, a torsion stress Tq2a in an opposite direction from the torsion moment Tq2 is generated in the instrument panel R/F pipe 104.
By setting to the same position the mounting positions of the floor brace 100 which primarily suppresses the torsion in the clockwise direction of the instrument panel R/F pipe 104 and the cowl-to brace 102 which primarily suppresses the torsion in the counterclockwise direction of the instrument panel R/F pipe 104, an amount of torsion of the instrument panel R/F pipe 104 is balanced between the time when a downward load is imposed on the steering wheel 110 and the time when an upward load is imposed on the steering wheel 110. Because the amount of torsion of the instrument panel R/F pipe 104 is reflected in an amount of displacement of the steering wheel 110, the amount of displacement of the steering wheel 110 can be balanced between the time of application of the upward load and the time of application of the downward load.
When the floor brace and the cowl-to brace are joined only to a part of the instrument panel R/F pipe around its circumference, there is a possibility of cross-sectional shape collapse (cross-sectional deformation) of the instrument panel R/F pipe. For example, as shown in FIG. 12, when a downward load F1 is applied to the steering wheel 110, a load pulling in the clockwise direction is applied to one end 112A of a non-joined portion 112 of the instrument panel R/F pipe 104. Similarly, a load to gather the material in the clockwise direction is imposed on the other end 112B of the non-joined portion of the instrument panel R/F pipe 104.
As a result, the non-joined portion 112 which is thinner compared to the joined portion 111 is deformed, and the cross-sectional shape collapse occurs in which the cross-sectional shape of the instrument panel R/F pipe 104 is deformed from the true circle shown by the broken line. As a result of the cross-sectional shape collapse, the rigidity of the instrument panel R/F pipe 104 may be reduced such as, for example, a reduction of the rigidity in the up-and-down direction in the example structure of FIG. 12.
An advantage of the present disclosure lies in provision of a steering support structure which can further suppress, compared to the related art, the cross-sectional shape collapse of the instrument panel R/F pipe when loads in the up-and-down direction are applied to the steering wheel.